1. Field of the Invention
This invention relates to a process and system for computing and adjusting the optimum ignition advance on an internal combustion engine by means of a device for detecting knocking.
2. Description of the Prior Art
High-performance engines, such as supercharged or high-compression engines, have a tendency under full load to knock at an ignition advance setting which is clearly lower than optimum. In view of the inconvenience and even the risk of destruction of the engine which the presence of knocking represents, it is necessary, when using a classic ignition system, to select a centrifugal ignition principle with a wide margin (on the order of four degrees) with respect to the advance which initiates knocking. This can translate into a great loss of efficiency which, because of limitations in the choice of centrifugal principles, has effects even in the zones where knocking does not occur.
It has already been attempted, in a number of variants, to resolve the above problem. The principles of all these variants are the following:
selection of a centrifugal principle close to the knocking point, or even past the knocking point; PA1 detection of the presence of knocking by measurement with an accelerometer and comparison with a threshold; PA1 more or less rapid reduction of the advance; PA1 instantaneous or progressive return to the nominal advance.
One of the problems with the recommended solutions lies in the choice of the threshold above which it is decided that there will be knocking. This choice must, in effect, take into consideration inter alia the differences between motors, variations in electronic gain, and the sensitivity of the sensor. This point is always delicate to adjust even in the case of so-called self-adapting thresholds.
In all of the prior art systems, the threshold chosen is the same for all cylinders of the engine. It is difficult to distinguish between knocking and the appearance of noises of mechanical origin. This is particularly true when one increases the sets of rockers.
The prior art systems only operate when in fact there is knocking. In the best cases, knocking cannot be totally eliminated, there remaining always a small number of knocks. This number may drop when the time for return to the nominal advance is increased, but then the engine remains longer in a zone of lowered efficiency.